Are devils worth 7 blood each?

[Cohen]

Clam is effectively strong, but you can handle a loner clamming if you're stronger.

But investing in clams requires a good amount of water gems, especially at starting. Sadly none can see you're clamming til lyou reveal your strenght, and this IMO is the bad thing.
If people could see you're raising your gem income every turn far beyond your province ownage chance by finding sites, probably will gang up unless they want to find themselves against dozens of horrors that run in a totally unpredictable way in your land, to have to face some wish empowered SCs or such. In a long term game you'll find yourself without any chance of global spell during more than 1 turn too.
The other bad stuff is that a scout can keep the clam and so is immune to most ranged spells and raiding (but usually they're inside a castle)
IMO Clams should work only on mages (they know how to take care of those trinkets and such) and the mage should be set to research (unless we want to change the clam working system, as the mage is required to do an action to "alchemize" the free pearls out from the clams he's bringing).